The passenger service ceased to operate when the ferry Hamnavoe suffered serious damage to one of the engines.
Publicly-funded Serco Northlink caused uproar when it failed to replace the vessel, instead re-routing passengers through Aberdeen – over 200 miles from Scrabster.
Serco NorthLink’s managing director Stuart Garrett has confirmed that, allowing for successful sea trials off Rosyth on Sunday, the Hamnavoe will return to Orkney on Monday and resume her timetabled service on Tuesday, three days earlier than expected.
He said that thanks to a gruelling round-the-clock schedule worked by the engineering teams the starboard engine has been repaired and refitted earlier than scheduled following a major crankshaft failure on 25 April.
The NorthLink freight vessel Helliar, which has provided continued regular freight travel between Orkney and Caithness while the Hamnavoe was out of service, will then return to its normal timetable.
Business leaders in both Caithness and Orkney claimed they had lost a huge amount of trade at the beginning of the tourist season because of the failure to replace the passenger service.
Transport Minister Keith Brown, who also came under fire for the Scottish Government’s position, said: “With sea trials due to take place on Sunday 19 May, and subject to them being carried out successfully, we would expect her back in Stromness on Monday evening, ready to take up her duties on Tuesday.
“I would like to thank the engineers for all of their hard work so far. I will of course continue to receive daily updates until the MV Hamnavoe is back on the Scrabster - Stromness route and look forward to seeing her back at work on the Pentland Firth very soon.”
Mr Garrett added: “I would like to thank the engineering team for working tirelessly to ensure this lifeline service is resumed ahead of schedule. I would also like to thank our customer service staff for ensuring all customers were offered alternative travel plans.
“It was disappointing to have to withdraw the Hamnavoe from service on 26 April after the crankshaft failed.
“We are confident the engineering works required to return the vessel to service will be completed over the weekend and we look forward to having the Hamnavoe back in Stromness in time for the Orkney Folk festival next week.”